In recent years, researchers have gained a deeper understanding of the effects of low-dose aspirin for the prevention of cardiovascular disease. It now appears that aspirin has different effects in men and women.

Among men, the benefits of aspirin are well documented. It has been shown to reduce the risk of first and second incidents of heart attack, while its effect on stroke prevention is less certain. If chewed within 30 minutes of the onset of a heart attack, aspirin has also been shown to reduce the damage to the heart muscle. Based on these findings, many leading medical groups, including the American Heart Association, recommended that aspirin therapy also be considered for prevention of heart disease among women in certain circumstances.

Until recently, however, there were few studies examining aspirin’s ability to protect women from cardiovascular events. In 2005, the results of the Women’s Health Study were released. This 10-year study examined low-dose aspirin use among nearly 40,000 women. Although smaller studies had found that aspirin was protective for men and women, the Women’s Health Study found that aspirin did not prevent first heart attacks, nonfatal stroke or death among women under the age of 65. The study did find, however, that aspirin helped prevent stroke and reduced the risk of heart attack in women over age 65.

Similarly, the study found that low-dose aspirin therapy had no effect on the risk of developing any variety of cancer among women, with the possible exception of lung cancer.

These results were generally reaffirmed by a meta-analysis published in early 2006 in the Journal of the Medical Association. To conduct a meta-analysis, researchers pool data from several existing studies. In this case, a team of researchers looked at data that included women from the Women's Health Study in addition to five other studies. In all, more than 95,000 people, including 44,114 men and 51,432 women, were enrolled in the studies. These studies found that aspirin prevents ischemic stroke in women, but had no effect on heart attacks. For men, the studies revealed that aspirin therapy reduced the risk of heart attack but did not prevent stroke.

More studies are needed to confirm these results. However, based on the uncertainty surrounding aspirin use and its possible side effects, women should not begin low-dose aspirin therapy unless under the direct supervision of a physician.

The study did not examine the effects of aspirin therapy on other conditions, such as high blood pressure that occurs during pregnancy or the use of aspirin among women who are suffering a heart attack.